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Fast scanning systems for Laser-wires. Alessio Bosco, G. A. Blair, S. T. Boogert, G. Boorman, L. Deacons, C. Driouichi, M. Price Royal Holloway University of London. Laser-wire Mini Workshop Oxford University 3 rd July 2006. 330ns (3MHz). distance between trains hundreds of ms (few Hz).

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fast scanning systems for laser wires
Fast scanning systemsfor Laser-wires

Alessio Bosco,G. A. Blair, S. T. Boogert, G. Boorman, L. Deacons, C. Driouichi, M. PriceRoyal Holloway University of London

Laser-wire Mini WorkshopOxford University 3rd July 2006

slide2

330ns

(3MHz)

distance between trains

hundreds of ms

(few Hz)

2800

bunches

(train length ~ 1 ms)

Task: scan over 10 consecutive bunches

scanner

z

slide3

330ns

(3MHz)

2800 bunches (train length ~ 1 ms)

ultra-high driving frequency:

with 3 MHz laser (to be developed in Oxford)

and 100 kHz scanner (RHUL job)

we could in principle scan every 4th group of 10 bunches

time of one complete scan = 3.3 ms

number of scan within a train 100

…possible with EO to run @ 300 kHz

(scan every group of 10 bunches)

slide4

2800 bunches (train length ~ 1 ms)

330ns

(3MHz)

Device’s driver idea:

top voltage few kV (for EO devices)

4th group

of bunches

1st group

of bunches

starting point 100 kHz (maybe 300…)

slide5

Electro-Optic Techniques:

high repetition rates

response time limited by voltage driver and electrical capacities

high reproducibility

no shifts of mirrors or other optics are needed

of course there are still many open issues…

slide6

n + Dn

Operation principle:

modify the refraction direction by changing

the refractive index via EO effect

slide7

Some Issues:

  • Low Efficiency of EO devices (Dn~10-5 with E=1 kV/cm)
  • High Applied Voltage (which might limit the working frequency)
  • Aperture of the device should be large enough to:
  • accommodate larger laser beam spot sizes
  • (ranged between 1 – 10 mm)
  • in order to have lower intensity (we aim to work with tens of MW), better focus, less diffraction…
  • - limit the device electrical capacity (faster time response)
  • but Electric Field is INVERSELY dependent on the thickness
slide9

a

qin

qout’

n=n0

n = n0 + Dn

Scanner working principle:

Electrodes should be deposed

over the triangular faces and

cover the WHOLE surface

(deflection happens at the edges!)

slide10

approx. 10 mm

a = 45 deg

Z axis

Deposed Electrodes

5 mm

prism aperture

approx. 11 mm

Scanner prototype (LNB):

slide11

Experimental set-up

Static voltage (up to 2 kV) tests:

slide12

V = 0

V = 1 kV

V = 2 kV

Experimental results:

scan range @ focus VS applied voltage

input spot = 2 mm

waist = 68 mm (135 diameter)

shift = 75 mm

deflection = 0.25 mrad

slide13

V = 0

V = 1 kV

V = 2 kV

Experimental results:

scan range @ focus VS applied voltage

input spot = 3 mm

waist = 46 mm (92 diameter)

shift = 52 mm

deflection = 0.17 mrad

slide14

V = 0

V = 1 kV

V = 2 kV

Experimental results:

scan range @ focus VS applied voltage

input spot = 2 mm

2.5X beam exp after the EO prism

waist = 26 mm (52 diameter)

shift = 31 mm

deflection = 0.1 mrad

slide15

RESULTS and PROBLEMS:

  • EO prism could be actually used as a scanning device.
  • The fundamental problem of beam distortion can be solved.
  • Deflection obtained was just one order smaller than

the typical obtainable with piezo-scanner (1-2 mrad).

  • Obtained shift ~1 times the waist; need 5-10 times the waist.
slide16

POSSIBLE SOLUTIONS:

  • Higher EO coefficient (available on the market)
  • Higher applied voltage – problems of high speed driving.
  • Increase the size of the prism in order to have larger spot

to be focused tighter – problem with the E-field)